Asking teenagers to make important decisions about exams and GCSE subject choices at age 14 is placing "a lot of responsibility" on youngsters whose brains are not yet fully developed, according to a leading scientist.

Sarah-Jayne Blakemore, a professor in cognitive neuroscience at University College London (UCL), suggested that adult expectations are being put on young people to make decisions about their futures at a certain stage of their education, when their opinions and preferences are still likely to change over time.

Under the current system, teenagers are asked to choose which subjects they want to take at GCSE when they are in Year 9 - usually aged 13 or 14.

Speaking at a science conference in London, which was examining the issues, Prof Blakemore said: "I don't think we should be making any kinds of choices at age 14, or at least we shouldn't be forcing children to make choices at age 14."

In the last 15 or 20 years, new developments and technologies have meant that scientists now have the ability to scan the living brain and track changes in its structure and function. That research has changed the way human brain development is viewed, she argued.

" We now know that the vast majority of the brain undergoes very protracted development throughout childhood, but also throughout adolescence and into the 20s, 30s, even the 40s in some cases."

One key region - the pre-frontal cortex, which is involved in abilities such as decision making, planning, impulse control, empathy and self-awareness, continues developing throughout the first three decades of life, and there is great capacity for change during this time, Prof Blakemore said.

"If you think back about what you were like age 14, I'm thinking about your music preferences, your clothes preferences, or even maybe your moral or political beliefs, I would bet for most people they change quite a lot. And that's true not for just your fashion tastes, but it certainly can be true for any kinds of preferences and that has a very established biological basis. That capacity for change during adolescence.

"Another way to think about this is you would never expect a six-year-old to make decisions about career choices or subject choices. And that's because we all know, six-year-olds are small and their brains and cognitive abilities just are not capable of making lifelong decisions, or decisions that might have an impact for the rest of their lives. And generally, parents or teachers make those kinds of decisions for six-year-olds.

"But we do place a lot of responsibility on 14-year-olds, I think that's partly because they kind of look like adults in a lot of cases and you put adult expectations on them. But actually, if you look in their brains, their brains are not yet like an adult brain, they have got a long way to go."

A teenager's brain is still developing for very good reasons, she told the SCORE annual conference, adding: "I n some ways, who wouldn't want a very plastic brain that is adaptable and can learn and is very creative and passionate, like a typical teenage brain."

But Prof Blakemore added: "O n the other hand, I think we do place much higher expectations on teenagers than perhaps we should, given the fact that their brains still have a lot of development time to go.

"I think that's the first reason, that summarises the capacity for change that we shouldn't force 14 year-olds to make decisions that will affect the rest of their lives. Especially because in this country, there's a kind of one-size-fits-all approach, it's very difficult to change your choices once you've made them.

"The second point is that I think it's really important to learn science up to age 18, because learning basic information about the scientific method empowers people to make informed decisions about health related choices, or issues that have some kind of scientific basis."

Prof Blakemore later said that she supported an International Baccalaureate (IB) style system. Sixth-formers taking the IB have to studying a wide range of subjects, including science, humanities and languages, with some studied to a greater depth than others.

SCORE is a partnership of science organisations that aims to improve science education in England's schools and colleges.